Wet abatement system for waste SiH4

ABSTRACT

A new method of silane abatement is achieved. The novel silane abatement system comprises a water-filled chamber within an outer chamber. An air intake is located in one upper portion of said outer chamber and an exhaust output is located in another upper portion of the outer chamber. A silane gas intake pipe runs into the outer chamber and has its output under water in the water-filled chamber. A drain is connected through a valve at a bottom portion of the water-filled chamber. Many safety features are built into the wet abatement system, including temperature and water level sensors, water sprinklers, and means for shutting off air supply, exhaust, and silane intake. Waste silane gas is bubbled into a water-filled chamber. The waste silane gas is reacted with oxygen in water in the water-filled chamber whereby SiO 2  precipitates are formed and wherein the SiO 2  precipitates settle to a bottom surface of the water-filled chamber. The SiO 2  precipitates are drained out of the water-filled chamber to complete the abatement process.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The invention relates to a method of and device for abatement ofwaste SiH₄ in the fabrication of integrated circuits, and moreparticularly, to a method of and device for safe wet abatement of wasteSiH₄ in the manufacture of integrated circuits.

[0003] (2) Description of the Prior Art

[0004] Chemical vapor deposition (CVD) processes are widely used inintegrated circuit manufacturing. For example, polysilicon or silicondioxide layers can be deposited by CVD using silane (SiH₄) gas or othersimilar gases. After the CVD process has been completed, excess silanegas remains in the CVD system. Typically, excess reactant gases areremoved by an exhaust system. The exhaust system may vent the reactantgas to the atmosphere. However, silane gas is pyrophoric and cannot bereleased into the atmosphere. Silanes and similar gases must be filteredfrom the exhaust gas stream or converted to compounds that can bedisposed of safely. A common method of converting waste silane to adisposable compound is through combustion in a so-called “burn box”. Inthe burn box, the SiH₄ is converted to SiO₂ by the reaction:2SiH₄+2O₂-->2SiO₂+4H₂. However, the risk is that the burn box may be asource of fire if system failure occurs suddenly. For example, if theexhaust system fails, residue SiH₄ will collect in the burn box makingit likely that an uncontrolled fire will start.

[0005] U.S. Pat. Nos. 6,174,349 to DeSantis, U.S. Pat. No. 6,126,906 toImamura, and U.S. Pat. No. 5,183,646 to Anderson et al describeprocesses and devices including burn boxes. Wet scrubbers and otherabatement methods are also used. U.S. Pat. No. 6,174,349 to DeSantisteaches a wet scrubber in combination with the burn box. U.S. Pat. No.5,955,037 to Holst et al shows an oxidation treatment. U.S. Pat. No.5,320,817 to Hardwick et al uses an amine-forming metal salt to scrubsilane.

SUMMARY OF THE INVENTION

[0006] Accordingly, a principal object of the present invention is toprovide an effective and very manufacturable method of silane abatementin the fabrication of integrated circuit devices.

[0007] Another object of the present invention is to provide aneffective and very manufacturable method of silane abatement wherein theabatement system does not present the danger of being a source of fire.

[0008] Another object of the invention is to provide a silane abatementsystem that does not present the danger of being the source of fire.

[0009] In accordance with the objects of this invention a new method ofsilane abatement is achieved. Waste silane gas is bubbled into awater-filled chamber. The waste silane gas is reacted with oxygen inwater in the water-filled chamber whereby SiO₂ precipitates are formedand wherein the SiO₂ precipitates settle to a bottom surface of thewater-filled chamber. The SiO₂ precipitates are drained out of thewater-filled chamber to complete the abatement process.

[0010] Also in accordance with the objects of this invention a newsilane abatement system is achieved. The silane abatement systemcomprises a water-filled chamber within an outer chamber. An air intakeis located in one upper portion of the outer chamber and an exhaustoutput is located in another upper portion of the outer chamber. Asilane gas intake pipe runs into the outer chamber and has its outputunder water in the water-filled chamber. A drain is connected through avalve at a bottom portion of the water-filled chamber. Many safetyfeatures are built into the wet abatement system, including temperatureand water level sensors, water sprinklers, and means for shutting offair supply, exhaust, and silane intake.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the accompanying drawings forming a material part of thisdescription, there is shown:

[0012]FIGS. 1 and 2 schematically illustrate in cross-sectionalrepresentation a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention provides a method and a device for wastesilane abatement. The waste silane abatement system of the presentinvention successfully deals with the waste silane without danger ofbeing a fire source. No burn box is used in the method and device of theinvention. Rather, waste SiH₄ gas is reacted with dissolved oxygen toform solid SiO₂ which can be disposed of safely. Safety features of thedevice of the present invention include sprinklers that will beautomatically triggered in the event of fire.

[0014]FIGS. 1 and 2 illustrate the waste SiH₄ abatement system of thepresent invention. Referring now to FIG. 1, waste abatement device 10 isshown. A portion of the device is filled with water 22. Oxygen gas isdissolved in the water 22. Waste SiH₄ gas enters the chamber 10 fromthrough a pressurized pipe 18. High pressure N₂ gas flow 19 pushes theSiH₄ gas through the pipe 18, into the chamber 10 and out through thepipe 24 under the water. N₂ gas here is used to prevent back fire to theprocess tool. If backfire occurs, N₂ is activated to push the fire intothe water chamber. The N₂ gas flow is at a high pressure of about 100psi.

[0015] The SiH₄ gas is bubbled into the water 22. FIG. 2 is a close-upof the pipe 24. The waste SiH₄ gas is pumped through pipe 18 into aC-shaped stainless steel square pipe 24. Flippers 14 are pushed upwardby pressure to release SiH₄ gas for reaction with dissolved O₂ forabatement. In water at 25° C., there is about 8.4 ppm of dissolved O₂.The gas reacts with dissolved oxygen in the water to form a heavyprecipitate of SiO₂. The SiO₂ precipitate sinks slowly to the base ofthe chamber. The drain valve 26 is opened, subject to the SiO₂ level, toclear the solid SiO₂ out through the drain 28. Most likely, the drainvalve may be opened once a day.

[0016] Chamber 20 provides for water overflow. Continuous fresh airintake 30 into the chamber 10 insures the process of oxygen dissolvinginto the water from the air is not interrupted. An open-ended drain 36in the chamber 20 will capture water over-flow from the water-filledsection 22 of the chamber. An exhaust pipe 38 is separated from thechamber 10 by an exhaust flipper 32. The exothermic abatement processmay release smoke into the chamber. This smoke is exhausted into thepipe 38. The exhaust pipe also provides forced air ventilation from thechamber outside into chamber 10 for the air dissolving process.

[0017] A controller 34 controls the water supply 42 and fusible link 44.The controller also monitors a water temperature sensor 46, a waterlevel sensor 48, and an exhaust temperature sensor 50. Water sprinklers52 located in the chamber ceiling and in the exhaust pipe are triggeredby the controller by a high water temperature, high exhaust pipetemperature, or when the fusible link is broken. The fusible link is aburnable material such as nylon. If this link is exposed to heat highenough to break it, the controller will turn on the water sprinklers.The water level sensor avoids “dry-run” operations if the water level isnot high enough.

[0018] If a minor explosion occurs within the chamber 10, the air intake30 and the exhaust flipper 32 will shut. The flippers are normally open,but will be pushed closed by the pressure of an explosion. The oxygensource will also be cut off to stop any fire. That is, the air intakeflipper 30, normally open, will be pushed closed by pressure due tofire. If the fusible link 49 within one or both of the N₂ high pressurepipes is broken, indicating high heat, high pressure N₂ flow 19 will betriggered to push the fire back into the water chamber 22 and to form N₂blanketing to stop a fire.

[0019] The wet abatement system of the present invention consists of awater-filled chamber within an outer chamber. An air intake flipper andan exhaust flipper control input and output of air. A drain is connectedthrough a valve to the water-filled chamber. An overflow drain is at thebottom of the outer chamber. A controller controls the water supply andmonitors the water level, water temperature, exhaust temperature, and afusible link within the exhaust pipe. A pipe brings waste SiH₄ gas intothe water-filled chamber. A high pressure pump pushes the waste gasthrough the pipe.

[0020] In the wet abatement process of the present invention, wastesilane gas is bubbled into the water-filled chamber of the wet abatementsystem of the present invention. N₂ gas at high pressure pushes thesilane gas through a pipe into the water-filled chamber. The silane gasreacts with oxygen dissolved in the water to form a precipitate of SiO₂.The SiO₂ settles to the bottom of the chamber and is removed from thechamber through a drain.

[0021] The process of the present invention abates waste SiH₄ in thewater state. The abatement system will not be a source of fire becauseof the safety features of the wet abatement system of the presentinvention. These safety features include: water sprinklers located onthe ceiling of the outer chamber above the water-filled chamber and inthe exhaust pipe, air intake and exhaust flippers that close in theevent of an explosion, a process pump trip, fusible links located withinthe exhaust pipe and within the N₂ pipes that will break if exposed tohigh heat, water temperature and exhaust temperature sensors, and awater level sensor. The controller monitors the sensors and the fusiblelinks. If either of the temperature sensors show a high temperature orif any of the fusible links are broken, the water sprinklers aretriggered, the air intake and exhaust flippers are closed, the oxygensupply into the chamber is cut off, and the N₂ gas pump is shut downafter pushing residue waste gas into the water-filled chamber. If thewater level sensor shows the water level is too low, the system is alsoshut down.

[0022] The process and device of the present invention provide wetsilane abatement without danger of fire from the abatement system. Thewet abatement system of the present invention has a variety of safetyfeatures that work together to provide safe and effective silaneabatement.

[0023] While the invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A silane abatement system comprising: awater-filled chamber within an outer chamber; an air intake in one upperportion of said outer chamber; an exhaust output in another upperportion of said outer chamber; a silane gas intake pipe running intosaid outer chamber and having its output under water in saidwater-filled chamber; and a drain connected through a valve at a bottomportion of said water-filled chamber.
 2. The silane abatement systemaccording to claim 1 wherein said output of said silane gas intake pipeis into a C-shaped stainless steel pipe having upwardly opening flipperswhereby silane gas is released into water within said water-filledchamber.
 3. The silane abatement system according to claim 1 whereinsaid air intake and said exhaust output both comprise inwardly openingflippers.
 4. The silane abatement system according to claim 1 furthercomprising an overflow drain at a bottom portion of said outer chamber.5. The silane abatement system according to claim 1 further comprising:a water supply pipe connected to said water-filled chamber; a waterlevel sensor connected to said water-filled chamber; and a watertemperature sensor connected to said water-filled chamber.
 6. The silaneabatement system according to claim 5 further comprising a controllerthat controls said water supply and monitors said water level sensor andsaid water temperature sensor.
 7. The silane abatement system accordingto claim 6 wherein in the event that said controller detects anunacceptable condition from either of said water level sensor or saidwater temperature sensor, said air intake and said exhaust output areclosed, and residue waste silane gas within said silane gas intake pipeis pumped into said water-filled chamber.
 8. The silane abatement systemaccording to claim 1 further comprising: an exhaust pipe exiting saidouter chamber through said exhaust output; an exhaust temperature sensorconnected to said exhaust pipe; and a fusible link within said exhaustpipe.
 9. The silane abatement system according to claim 8 wherein in theevent that an unacceptable condition is detected in either of saidexhaust temperature sensor or said fusible link, said air intake andsaid exhaust output are closed, and residue waste silane gas within saidsilane gas intake pipe is pumped into said water-filled chamber.
 10. Thesilane abatement system according to claim 1 further comprising a highpressure pump connected to said silane gas intake pipe.
 11. The silaneabatement system according to claim 10 wherein said high pressure pumpprovides N₂ gas for pushing silane gas through said gas intake pipe intosaid water-filled chamber.
 12. The silane abatement system according toclaim 1 further comprising a fusible link within said high pressurepump.
 13. The silane abatement system according to claim 1 furthercomprising water sprinklers on an upper portion of said outer chamberand over said water-filled chamber.
 14. The silane abatement systemaccording to claim 1 further comprising water sprinklers on surfaces ofsaid exhaust pipe.
 15. The silane abatement system according to claim 1wherein waste silane gas is abated by: bubbling silane gas through saidsilane gas intake pipe and into said water-filled chamber; reacting saidsilane gas with oxygen dissolved in water in said water-filled chamberwhereby SiO₂ precipitates are formed and wherein said SiO₂ precipitatessettle to a bottom surface of said water-filled chamber; and openingsaid valve to drain said SiO₂ precipitates out of said water-filledchamber through said drain.
 16. A silane abatement process comprising:bubbling waste silane gas into a water-filled chamber; reacting saidwaste silane gas with oxygen dissolved in water in said water-filledchamber whereby SiO₂ precipitates are formed and wherein said SiO₂precipitates settle to a bottom surface of said water-filled chamber;and draining said SiO₂ precipitates out of said water-filled chamber.17. The process according to claim 16 further comprising flowing N₂ gasat high pressure to push said waste silane gas into said water-filledchamber.
 18. A silane abatement system comprising: a water-filledchamber within an outer chamber; an air intake in one upper portion ofsaid outer chamber; an exhaust output in another upper portion of saidouter chamber connecting to an exhaust pipe; water sprinklers on anupper portion of said outer chamber and over said water-filled chamberand on surfaces of said exhaust pipe; a silane gas intake pipe runninginto said outer chamber and having its output under water in saidwater-filled chamber; and a drain connected through a valve at a bottomportion of said water-filled chamber.
 19. The silane abatement systemaccording to claim 18 wherein said output of said silane gas intake pipeis into a C-shaped stainless steel pipe having upwardly opening flipperswhereby silane gas is released into water within said water-filledchamber.
 20. The silane abatement system according to claim 18 whereinsaid air intake and said exhaust output both comprise inwardly openingflippers.
 21. The silane abatement system according to claim 18 furthercomprising an overflow drain at a bottom portion of said outer chamber.22. The silane abatement system according to claim 18 furthercomprising: a water supply pipe connected to said water-filled chamber;a water level sensor connected to said water-filled chamber; a watertemperature sensor connected to said water-filled chamber; an exhausttemperature sensor connected to said exhaust pipe; a fusible link withinsaid exhaust pipe; and a controller that controls said water supply andmonitors said water level sensor, said water temperature sensor, saidexhaust temperature sensor, and said fusible link.
 23. The silaneabatement system according to claim 18 further comprising a highpressure pump connected to said silane gas intake pipe having a fusiblelink within said high pressure pump.
 24. The silane abatement systemaccording to claim 18 wherein waste silane gas is abated by: bubblingsilane gas through said silane gas intake pipe and into saidwater-filled chamber; reacting said silane gas with oxygen in water insaid water-filled chamber whereby SiO₂ precipitates are formed andwherein said SiO₂ precipitates settle to a bottom surface of saidwater-filled chamber; and opening said valve to drain said SiO₂precipitates out of said water-filled chamber through said drain. 25.The silane abatement system according to claim 22 wherein in the eventthat said controller detects an unacceptable condition from any of saidwater level sensor, said water temperature sensor, said exhausttemperature sensor, or said fusible link, said water sprinklers aretriggered, said air intake and exhaust flippers are closed, and residuewaste silane gas within said silane gas intake pipe is pumped into saidwater-filled chamber.